Wolbachia co-infection in a hybrid zone: discovery of horizontal gene transfers from two Wolbachia supergroups into an animal genome.

Lisa J Funkhouser-Jones,Paloma Martínez-Rodríguez,Raquel Toribio-Fernández,José L Bella,Miguel Pita,Seth R Bordenstein,Stephanie R Sehnert

doi:10.7717/peerj.1479

Abstract

Hybrid zones and the consequences of hybridization have contributed greatly to our understanding of evolutionary processes. Hybrid zones also provide valuable insight into the dynamics of symbiosis since each subspecies or species brings its unique microbial symbionts, including germline bacteria such as Wolbachia, to the hybrid zone. Here, we investigate a natural hybrid zone of two subspecies of the meadow grasshopper Chorthippus parallelus in the Pyrenees Mountains. We set out to test whether co-infections of B and F Wolbachia in hybrid grasshoppers enabled horizontal transfer of phage WO, similar to the numerous examples of phage WO transfer between A and B Wolbachia co-infections. While we found no evidence for transfer between the divergent co-infections, we discovered horizontal transfer of at least three phage WO haplotypes to the grasshopper genome. Subsequent genome sequencing of uninfected grasshoppers uncovered the first evidence for two discrete Wolbachia supergroups (B and F) contributing at least 448 kb and 144 kb of DNA, respectively, into the host nuclear genome. Fluorescent in situ hybridization verified the presence of Wolbachia DNA in C. parallelus chromosomes and revealed that some inserts are subspecies-specific while others are present in both subspecies. We discuss our findings in light of symbiont dynamics in an animal hybrid zone.

Highlights

Microbial communities of many arthropod species are dominated numerically by heritable bacterial symbionts whose phenotypic effects range from mutualism to parasitism (Douglas, 2011)
Infected and uninfected grasshoppers across the hybrid zone harbor phage WO genes To initially determine the prevalence of phage WO in the C. parallelus hybrid zone, we PCR-screened hybrid, C. parallelus erythropus (Cpe), and C. parallelus parallelus (Cpp) grasshoppers of all infection types for the minor capsid gene, a virion structural gene commonly used to identify WO haplotypes (Bordenstein & Wernegreen, 2004; Chafee et al, 2010; Gavotte et al, 2004; Masui et al, 2000)
Blank controls were negative for the orf7 amplicon. These results indicate that (i) phage WO is or once was ubiquitous in C. parallelus and (ii) at least part of phage WO has laterally transferred to the grasshopper genome

Summary

Introduction

Microbial communities of many arthropod species are dominated numerically by heritable bacterial symbionts whose phenotypic effects range from mutualism to parasitism (Douglas, 2011). Millennia of co-evolution have produced obligate, mutualistic relationships in which microbial symbionts make essential amino acids and/or. Maternally-transmitted bacteria directly impact arthropod host reproduction by manipulating sex determination, fecundity, and the ratio of infected females (the transmitting-sex) within a population (LePage & Bordenstein, 2013). The alphaproteobacterium Wolbachia is the most widespread of these reproductive manipulators, infecting an estimated 40–52% of all terrestrial arthropod species (Weinert et al, 2015; Zug & Hammerstein, 2012). It uses a variety of mechanisms to increase the number of host females in a population including feminization of genetic males, male-killing, parthenogenesis, and cytoplasmic incompatibility (CI), which typically results in embryonic death of offspring produced by an uninfected female mated with an infected male (Serbus et al, 2008)

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Conclusion